(1) Field of the Invention
The present invention relates to a proximity switch of the high frequency oscillation type and particularly pertains to an approach switch equipped with a signal detector circuit inserted in a cable connecting a detector head and a power source.
(2) Description of the Prior Art
Recently, high frequency oscillation type proximity switches are widely in use.
In the proximity switch of high frequency oscillation type, a signal detector circuit including a high frequency oscillator circuit, a detector circuit, a wave form shaping circuit, a comparator circuit, a reference voltage generator circuit, and an output circuit, etc., is used.
FIG. 1 shows a conventional proximity switch of the high frequency oscillation type, in which a detector head 2 having a coil 21 contained therein and a signal detector circuit 3 are interconnected through a cable 1. In this figure, reference numeral 31 denotes a power supply input line to the signal detector circuit and 32 is a signal line showing "ON" or "OFF" of the proximity switch.
In this proximity switch, the signal detector circuit 3 is housed in a relatively large boxy case. On this account, installing the case housing the signal detector circuit 3 in the vicinity of the detector head 2 will be objectonable because of increased spatial restriction in using the proximity switch. It is for this reason that the detector head 2 and the signal detector circuit 3 are normally installed apart from each other. Consequently, the cable 1 connecting the detector head 2 and the signal detector circuit 3 needs to be long, thus tending to be affected by noise. This separation of the signal detector circuit 3 and the detector head 2 from each other usually requires taking the trouble of connecting the signal detector circuit 3 and detector head 2 by wiring, every time this proximity switch is to be used.
FIG. 2 depicts a conventional proximity switch of the high frequency oscillator type which has been proposed and practically used for overcoming the above problem. The proximity switch in FIG. 2 is of a type having the signal detector circuit 3 provided within the detector head 2. Proximity switches of this type involve a disadvantage that the larger detector head is more likely to be subject to spatial restriction, although the inducement of noise and the troublesome wiring are averted.